Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to the implementation of telecommunication service in a data network on behalf of mobile wireless nodes. More particularly, the invention pertains to a system and method for routing data network communication content to mobile wireless nodes that are undergoing call hand off from one radio base station to another.
2. Description of the Prior Art
Considerable attention has been directed toward the implementation of mobile telecommunication service in computer data networks, and particularly the ability to route communication content to mobile wireless nodes that routinely connect to the data network at different points of attachment, via air interfaces. These include cellular telephones, Personal Digital Assistants (PDAs), laptop computers, and other mobile wireless communication equipment.
To facilitate mobile wireless telecommunication service in a data network, it is desirable (although not always possible) to allow mobile wireless nodes to change their link-layer point of network attachment without reassigning a new network address. According to current data network telecommunication standards for mobile equipment in general (e.g., the xe2x80x9cMobile IPxe2x80x9d standards promulgated by the Internet Engineering Task Force (IETF) or the General Packet Radio Service (GPRS) standards proposed by the European Telecommunication Standards Institute (ETSI)), one way to provide the desired network address transparency is to employ xe2x80x9cmobility agents.xe2x80x9d These are network routing nodes that route communication content on behalf of mobile nodes as they move around the network. For example, according to the IETF Mobile IP standards, a mobile node""s mobility agents may consist of a xe2x80x9chome agentxe2x80x9d routing node and may also include a xe2x80x9cforeign agentxe2x80x9d routing node. The home agent is a routing node in the mobile node""s subnetwork that maintains a network interface on the link indicated by the mobile node""s xe2x80x9chome address,xe2x80x9d which is a network address intended to remain assigned to the mobile node for an extended time period. When the mobile node is away from its home subnetwork, the home agent intercepts communication content bound for the mobile node""s home address and tunnels it for delivery to a xe2x80x9ccare-ofxe2x80x9d address assigned to the mobile node when the mobile node registers on a foreign subnetwork. The care-of address may be the address of a foreign agent routing node in the foreign subnetwork.
Correspondent nodes wishing to communicate with a foreign-registered mobile node are able to address their communication content to the mobile node""s home address. Transparently, the communication content is tunneled to the mobile node""s care-of address and delivered to the mobile node on the foreign subnetwork. Normal routing is used for sending return communication content from the mobile node to the correspondent node.
The foregoing routing mechanism can be used for mobile wireless nodes connected to a foreign subnetwork via an air interface. However, a problem may arise if the mobile wireless node is being actively transported while communicating over the data network, and a call handoff is required from one radio base station to another. In that case, the old base station may be linked to one care-of address, while the new base station is linked to another care-of address. Call handoff then requires that the communication tunneling endpoint be transferred from the old care-of address to the new care-of address.
This may create gaps that interrupt the timely delivery of call content, which can degrade communication quality, particularly for voice telephony. Such gaps arise from the inability of the data network to coordinate well with the air interface so as to determine the exact time of handoff. Delay can occur between the point of handoff and the point at which the home agent begins routing communication content to the new care-of address.
Accordingly, there is a need in a data network telecommunication system serving mobile wireless nodes for improved call handoff without loss of communication content. What is required is a system and method that seamlessly routes communication content during handoff so that the mobile wireless node does not experience noticeable communication content loss other than that caused by the air interface, if any.
A system and method in accordance with the invention provides seamless data network telecommunication service to a mobile wireless node during mobile wireless call handoff from a first radio base station to a second radio base station. Prior to call handoff, communication content addressed to the mobile wireless node is routed on behalf of the mobile wireless node to a first address for delivery to the mobile wireless node via the first base station. Upon initiation of the call handoff, the communication content is routed to a second address for delivery to the mobile wireless node via the second base station. At the same time, routing of the same communication content to the first address is continued. Upon completion of the call handoff, communication content routing to the first address is terminated.
In preferred aspects of the invention, it is contemplated that routing to the first and second addresses will be performed by a network routing node that acts on behalf of the mobile wireless node. If the invention is incorporated in a mobile networking environment as envisioned by the IETF Mobile IP standards, it is contemplated that the routing node will be implemented as a xe2x80x9chome agentxe2x80x9d that is located on the mobile wireless node""s home subnetwork, and which is configured to route communication content to designated care-of addresses as the mobile wireless node moves between cells served by the first and second base stations. In the IETF Mobile IP embodiment of the invention, it is contemplated that the care-of addresses will correspond to xe2x80x9cforeign agentsxe2x80x9d that are linked to, or reside at, the first and second base stations.
Finally, it will be understood that the mobile wireless node may communicate with correspondent nodes located in a data network, such as a LAN or WAN, or an internetwork, such as the public Internet, or communicate with telecommunication equipment connected to a voice network, such as the PSTN. The term xe2x80x9cdata networkxe2x80x9d as used herein is not intended to be limited in any way and should be understood as broadly including any system that allows data communication to occur by and between one or more data communication resources linked by one or more communication pathways.